This invention relates to a mixture containing one or more olefin rubbers and one or more nitrile rubbers, to a process for the production thereof, to a vulcanizable mixture and to a process for the production thereof as well as to moldings of all kinds producible from the mixtures.
Mixtures (blends) of incompatible elastomers are frequently encountered in industrial rubber articles. In general, the polymer components are mixed in a single mixing operation together with conventional additives without any particular measures being implemented to improve phase structure.
It is often observed in such processes that the expected improvements in certain material properties are accompanied by considerable disadvantages in other properties which are the result of insufficiently uniform distribution of the polymer phases in the blends. Mixtures containing EPDM may be taken by way of example. In mixtures with nitrile rubber (NBR), EPDM primarily improves low temperature flexibility. In contrast, other properties, such as vulcanizate strength and oil swelling, are impaired.
Improved mixing processes provide complicated, often multistage processes which are time-consuming and entail excessive mixing costs.
Mixtures of olefin polymers with nitrile rubbers are known, for example, from EP-A2-0 146 068, EP-A1-0 773 255 and U.S. Pat. No. 3,492,370. Although, macroscopically, these mixtures appear homogeneous, extensive domains of disperse phases are clearly evident on examination by phase-contrast microscopy (FIG. 1).
Therefore, the object of the present invention is to provide a mixture of olefin rubber and nitrile rubber having improved properties.
This object is achieved by a mixture containing one or more olefin rubbers and one or more nitrile rubbers, characterized in that there is no phase segregation in the mixture.